The Pentagon has banned four journalists from covering military commissions at Guantanamo Bay because they published the name of a witness after being told he must only be identified as "Interrogator No 1".

In an email to their editors, Pentagon spokesman Colonel Dave Lapan explained the ban by writing: "Your reporters published the name of a witness whose identity was protected in court."

The trial they were covering was of Omar Khadr, a 23-year-old Canadian prisoner who is charged with killing a US soldier in Afghanistan.

All four news organisations said they would appeal against the ban, which one called "absurd". They pointed out that the interrogator's name has been in the public domain since 2005, when he was convicted by a court martial of abusing detainees in Afghanistan in 2005.

He was publicly identified as Khadr's interrogator in March 2008, during a hearing at Guantanamo, and subsequently gave an on-the-record interview to Shephard.